In a large bowl, combine the flour and salt.
Add the cold, cubed butter and use your fingers or a pastry cutter to mix until the mixture resembles coarse crumbs.
In a small bowl, beat the egg with the cold water.
Gradually add the egg mixture to the flour mixture, mixing until a dough forms. If the dough is too dry, add a little more cold water, one tablespoon at a time.
Shape the dough into a ball, wrap it in plastic wrap, and refrigerate for at least 1 hour.
In a large skillet, heat the olive oil over medium heat.
Add the finely chopped onion and minced garlic and cook until softened, about 5 minutes.
Add the ground beef and cook until browned, breaking it up with a spoon as it cooks.
Stir in the chopped olives, raisins (if using), chopped hard-boiled eggs, ground cumin, smoked paprika, salt, and black pepper.
Cook for another 5 minutes, then remove from heat and let cool.
Preheat your oven to 375°F (190°C).
On a lightly floured surface, roll out the dough to about 1/8 inch (3 mm) thick.
Use a round cutter or a glass to cut out circles of dough, about 4-5 inches (10-12 cm) in diameter.
Place a spoonful of the filling in the center of each dough circle.
Fold the dough over the filling to create a half-moon shape.
Press the edges together firmly to seal, then crimp the edges with a fork or pinch them decoratively.
Place the empanadas on a baking sheet lined with parchment paper.
Brush the tops with the beaten egg.
Bake in the preheated oven for 20-25 minutes, or until the empanadas are golden brown.
Enjoy your meal!